The optical transmission technology makes the high speed communication possible and is much noted.
As a material of the optical fibers for the optical communication, conventionally quartz has been dominantly used. The optical fibers of quartz have very little attenuation of light, and are applicable to the long-distance optical communication.
However, the optical fiber of quartz is relatively expensive. The optical fiber of quartz has a core diameter as small as 10 μm for the single mode and a core diameter as small as 50 μm for the multi mode, which makes the alignment difficult.
Recently, optical fibers of plastics are proposed. The optical fiber of plastics is not so suitable for the long-distance communication but is less expensive in comparison with the optical fiber of quartz. The optical fiber of plastics has a core diameter as large as, e.g., φ120 μm, which facilitates the alignment.
To concurrently transmit a plurality of light signals, an optical fiber array having a plurality of optical fibers arranged in an array is used. Since the outer diameter of the optical fiber of plastic is generally φ500 μm or above, a pitch of the optical fiber array of these optical fibers is 500 μm or above.
However, the standard pitch of the plastic optical fiber (POF) array is 500 μm or above, but the conventional light emitting element array and light receiving element array, i.e., the conventional optical element array is 125 μm or 250 μm. Accordingly, the plastic optical fiber array and the optical element array cannot be optically connected directly with each other.
The standard pitch of the light emitting element array and the light receiving element array is 125 μm or 250 μm so as to ensure the alignment with the conventional optical fiber array of quartz, whose standard pitch is 125 μm or 250 μm.
Here, it is an idea to fabricate a new optical element array of a 500 μm-pitch. When the pitch of the optical element array is 500-μm pitch, the number of the optical element arrays which can be accommodated on one wafer is small, which makes the cost of the optical element array high. The 500 μm-pitch optical element array is not mass-produced, which makes the optical element array expensive. Accordingly, it is preferable to use the 250 μm-pitch optical element array which is universal.
As techniques of optically coupling an optical fiber array and an optical element array having different pitches, the following techniques are proposed.
That is, Patent Reference 1 proposes the technique that an optical waveguide for converting a pitch is disposed between an optical fiber array and an optical element array, whereby the optical fiber array and the optical element array having different pitches are optically connected.
Patent Reference 2 proposes the technique that an imaging lens is disposed between an optical fiber array and an optical element array so as to use an imaging magnification for the pitch conversion.
Patent Reference 3 proposes the technique that a block body with tilted optical fibers buried in is used for the pitch conversion.
[Patent Reference 1]
Specification of Japanese Patent Application Unexamined Publication No. Hei 11-119066
[Patent Reference 2]
Specification of Japanese Patent Application Unexamined Publication No. 2002-221642
[Patent Reference 3]
Specification of Japanese Patent Application Unexamined Publication No. 2001-24213
[Patent Reference 4]
Specification of Japanese Patent Application Unexamined Publication No. Hei 9-127375
[Patent Reference 5]
Specification of Japanese Patent Application Unexamined Publication No. 2002-329935
However, the proposed techniques described above are all cumbersome and cannot meet the requirements of small size and low cost. Especially, in the technique proposed in Patent Reference 2, because of the imaging lens, the alignment is very difficult. In the technique proposed in Patent Reference 3, the steps of forming the block body are complicated, which adds to the cost.
An object of the present invention is to provide an optical element which can optically connect an optical element array, an optical waveguide array, etc. having pitches different from each other, and an optical transmission unit and an optical transmission system using the optical element.